We wrote an article about our top 5 favorite free stock photo sites. With millions of photos and videos that can be downloaded with CC0 licensing, your real estate marketing materials can be completely unique and beautiful.
Our number one is Unsplash.com but the other 4 stock photo sites listed are also very useful.
Here is a quick tip, make sure you spend a bit longer time finding your perfect photo by searching for long-tail keywords to obtain unique pictures. E.g. search for "kitchen" or "door" or "kids playing" instead of "house" or "real estate"